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This article presents two cases of a progressive form of Coats' disease which were detected by local optometrists and successfully treated by ophthalmologists. Coats' disease is an exudative vasculopathy characterised by the presence of dilated retinal blood vessels (telangiectasia), micro-aneurysm formation, retinal exudation and exudative retinal detachment.
The disease manifests unilaterally in 80 to 90 per cent of cases, without evidence of racial or familial predilection.1 Bilateral asymmetrical involvement may also take place in rare occasions. Therefore, long-term follow up of the least affected eye is necessary so late complications can be identified earlier and treated to prevent visual loss.2
The disease usually presents between 18 months and 18 years, and 69-85 per cent of cases are male however, it can occur in females. It was shown that Coats' disease has a recurrent nature, so follow-up is very important throughout patients' adult life.3 There have been reported cases of the condition being diagnosed in advanced stages in low birth-weight infants. It is important to stress that early diagnosis and treatment can stabilise and improve the outcome.4 This condition has also been documented in adulthood with a number of important differences in disease manifestation, including limited area of involvement and slower apparent progression of disease.5
Aetiology
The aetiology of Coats' disease is unknown. However, there are some hypotheses of a genetic component, which were described by Genkova, Skuta and Black.6 Authors hypothesised that the NDP-encoded protein (norrin) played a key role in normal retinal angiogenesis and suggested that somatic mutation in the NDP gene caused abnormal retinal vascular development (telangiectasia) in Coats' disease.
Clinical signs and classification
Initially, Coats' disease presents with poor vision, leukocoria due to exudative retinal detachment (Figure 1), strabismus and intraocular masses, which could be detected by an optometrist on a routine eye examination. Shields proposed five stages of this condition based on selection of treatment and prediction of ocular and visual outcomes.7
? Stage 1 is characterised by the presence of telangiectasia (Figure 2). At this stage, patients are systematically observed or, if necessary, photocoagulation is used. Visual prognosis is usually encouraging.
? Stage 2 is subdivided into two types (2A and 2B) and characterised by the presence of telangiectasia and exudation. In stage 2A, there is no foveal exudation and the visual prognosis is generally good (Figure 3a). In stage 2B the visual prognosis worsens when the foveal exudation reaches its advanced level (Figure 3b). In this stage photocoagulation or cryotherapy are the options of treatment.
? Stage 3 is also subdivided into two (3A and 3B). In stage 3A, retinal detachment with foveal involvement can be resolved if telangiectasia is eliminated (Figure 4a). Cryotherapy is more effective than photocoagulation if exudative retinal detachment occurs. In stage 3B, a total retinal detachment takes place (Figure 4b). Surgical treatment is advised at this stage.
? Stage 4 requires enucleation of the eye secondary to neovascular glaucoma and severe ocular pain.
? Stage 5 involves management and treatment of an end-stage blind eye and care of the better seeing eye.
Case 1
A 13-year-old girl noticed reduced vision in her left eye, which progressively deteriorated within two months. On first examination her vision was 6/9 in both eyes. Two months later her visual acuity in the right eye was 6/12 improving with pinhole to 6/9 and in the left dropped to hand movements. The anterior segments were unremarkable. The right fundus was normal (Figure 5a). The left fundus examination showed sub-retinal lipid exudation in the temporal retina with a peripheral sub-retinal mass associated with vascular dilation and early stages of tractional maculopathy (Figure 5b). In order to prevent total retinal detachment, left vitrectomy with laser photocoagulation was performed.
Case 2
An eight-year-old boy initially presented with 6/12 in his right eye secondary to astigmatism. One year later his vision further decreased to 6/60 in the right eye and 6/6 in the left. The anterior segments were normal. Fundus examination showed massive exudation in the right inferior retina, spreading peripherally with overlying dilated and tortuous retinal blood vessels (Figure 6a). The left fundus was normal (Figure 6b). To resolve exudation and prevent neovascularisation and secondary retinal detachment, retinal cryotherapy was performed in the inferior quadrant of the retina. The result of treatment showed 70 per cent resolution of subretinal fluid and improvement of vision to 6/9.
Differential diagnosis
There are many other ocular conditions that mimic Coats' disease. The most common is retinoblastoma. Both conditions may occur with retinal detachment and abnormal blood vessels. However Coats' disease presents in the later stage of the first decade of life and has male predilection. Retinoblastoma is in 40 per cent heritable (germline) and in 60 per cent non-heritable (somatic) and clinically shows the presence of solitary tumour between the age of 13-24 months (Figure 7). Where there is a total retinal detachment, Coats' disease displays telangiectasia and yellow sub-retinal fluid whereas a sub-retinal space full of grey-white material is seen in retinoblastoma.8
Other common diseases which occur in the first two decades of life are:
? Retinopathy of pre-maturity (ROP)
? Persistent hyperplastic primary vitreous (PHPV), (Figure 8)
? Inflammatory cyclitic membrane
? Toxocara granuloma
? Retinal astrocytoma (Figure 9)
? Congenital cataract.
In older children and adults Coats' disease maybe confused with:
? Retinal vein occlusion
? Diabetic retinopathy
? Eales' disease
? Vasculitis
? Arterial macroaneurysm
? Melanoma
? Choroidal metastasis
?Choroidal and capillary haemangioma.
Investigations
At presentation it is important to collect accurate data regarding the patient's general health (low birth-weight infants3), medical and family history. This can help exclude other conditions such as ROP, retinoblastoma and other types of exudative retinopathy.
The condition is diagnosed by the appearance of the posterior pole of the eye using:
? Direct and indirect ophthalmoscopy
? Fluorescein angiography
? Ultrasonography
? CT scan.
Fundus examination with indirect ophthalmoscopy, fundus photography and fluorescein angiography are very important diagnostic procedures which help to differentiate Coats' disease from retinoblastoma.
Ultrasonography is the principal auxiliary diagnostic test and can be used repeatedly without any biologic tissue hazard. It allows the topography and character of retinal detachment and the presence/absence of sub-retinal calcification to be used to differentiate between Coats' disease and retinoblastoma.
CT scan is used to delineate intraocular morphology, quantify sub-retinal densities and detect calcification, associated orbital or intracranial abnormalities. The CT scan also allows the identification of vascular tissue within the sub-retinal space, by enhancing the contrast.
Treatment
The treatment options for Coats' disease depend on its stage and extent. The purpose of treatment is directed towards closure of the abnormal leaking retinal vessels to facilitate the resolution of exudation and retinal detachment.
If the disease is limited it is usually just observed. In case of further progression, treatment can range from scatter laser photocoagulation to cryotherapy. Aggressive treatment with cryotherapy before retinal detachment is likely to stabilise vision and decrease the risk of future total retinal detachment.9
In the advanced case of vitreous haemorrhage or retinal detachment, a pars plana vitrectomy or scleral buckling procedure is indicated for draining the sub-retinal fluid and re-attaching the retina.
Conclusion
One quarter of cases with Coats' disease are detected in asymptomatic patients during routine eye examination. This disease is the prime reason why optometrists should routinely dilate asymptomatic young patients. Early and appropriate treatment makes it possible to improve the outcome. ?
References
1 Smithen LM, Brown GC, Brucker AJ, Yannuzzi LA, Klais CM and Spaide RF. Coats' disease diagnosed in adulthood. Ophthalmology, 2005 June 112(6):1072-8.
2 Deepak PE, Mahmood FM et al. Coats' disease and persistent hyperplastic primary vitreous. Role of MR imaging and CT Radiologic. Clinics of North America, 1998 36:1119-1131.
3 Shienbaum G and Tasman WS. Coats' disease: a lifetime disease. Retina, 2006 April 26(4):422-4.
4 Alexandridou A and Stavrou P. Bilateral Coats' disease: long term follow up. Acta Ophthalmol Scand, 2002 Feb 80(1):98-100.
5 Maruoka K, Yamamoto M, Fujita H, Tahara Y and Ishibashi T. A case of Coats' disease in a low-birth-weight infant. Ophthalmologica, 2005 Nov-Dec 219(6):401-3.
6 Black GC, Perveen R, Bonshek R, Cahill M, Clayton-Smith J, Llloyd IC, McLeod IC and McLeod D. Coats' disease of the retina (unilateral retinal telangiectasis) caused by somatic mutation in the NDP gene: a role for norrin in retinal angiogenesis. Hum Mol Genet, 1999 8:2031-2035.
7 Shields JA,Shields CL, Honavar SG, Demirci H, Cater J. Classification and management of Coats' disease:the 2000 Proctor lecture. Am J of Ophthalmol, 2001 131: 572-583.
8 Campbell FP Coats' disease and congenital vascular retinopathy. Trans Am Ophthalmol Soc, 1977 74:365-412
9 Budning AS, Heon E and Gallie BL. Visual prognosis of Coats' disease. J AAPOS, 1998 Dec 2(6):356-9.
? Dr Irina Gout, Jo-Sheetal Thethy, optometrist, and Mr Sundeep Kheterpal, consultant ophthalmic surgeon, are based at The Prince Charles Eye Unit, King Edward VII Hospital, Windsor